Texas Equine Veterinary Association

www.texasequineva.com | 11 further diagnostics, paring the foot out extensively is necessary to identify the penetration site. Regional anesthesia is necessary not only to identify the region of the limb that the lameness arises from but to facilitate the paring of the penetration site, allowing the horse to weight bear for ease of radiography, and to facilitate synoviocentesis and positive contrast radiography of the three synovial structures in this area (Smith and Schramme 1992). Complete radiographic examination of the foot should always be performed to check for penetration of radio-opaque foreign objects, fractures, gas in the synovial structures, and in chronic cases, osteomyelitis or osteitis. If the horse is amendable and the foot can be padded, leaving the offending foreign object in place can aid in diagnosis of the penetration. Otherwise aer preparation of the foot, a malleable probe can be used to determine direction and location of the penetrating object. Examination of the distal limb can yield additional diagnostic information when determining the proper treatment for these wounds. Ultrasonography through the palmar/plantar aspect of the pastern and via a transcuneal window can image the proximal and distal portions of the navicular apparatus respectively (Busoni and Denoix 2001). e transcuneal window is quite unreliable in the author's hands to reliably obtain diagnostic images. However, the use of ultrasonography is quite reliable in detecting non-metallic foreign bodies and assessing synovial structures and deeper so tissue structures. Synoviocentesis is essential in determining the treatment protocol and assessing the prognosis of the injury. Oen there are multiple synovial structures that can be penetrated during a foot wound and misdiagnosis of a penetration can lead to failure of treatment. As previously stated, regional anesthesia can facilitate synoviocentesis. Synoviocentesis is essential in three ways; synovial fluid collection can help facilitate synovial fluid analysis to determine sepsis versus inflammation, synovial distension with sterile saline to determine communication with the wound, and to treat the synovial structure. All three can be accomplished with a single needle penetration of the synovial structure. Synovial fluid analysis is very important in aiding the treatment of the wounds. e gold standard for diagnosis of a septic structure is positive bacterial culture. However, in clinical practice this is oen impractical. Culture results can take anywhere from 24 to 48 hours. In addition, cultures from septic joints are negative in 45 to 77% of clinical cases when enrichment media is not used and are negative in 27 to 72% when it is used (Dumoulin et al. 2010). Regardless, it is recommended to submit synovial fluid in enriched media for culture and sensitivity as this can help guide antimicrobial therapy in difficult cases. e physical and cytological appearance of the synovial fluid can also help determine whether there is bacterial contamination of the joint. Visual examination is oen accurate in determining the presence of synovial contamination (Wright et al. 2003). Protein is consistently increased above 20 g/l, and oen >40 g/l (Wright et al. 2003). Total nucleated cell count is typically elevated and oen exceeds 50 x 109/l (Schneider et al. 1992; Wright et al. 2003). Neutrophils are the predominant cell type and frequently exceed 90% of the white cell differential (Wright et al. 2003). Serum Amyloid A elevation above 100 μg/mL is highly consistent with septic arthritis (Ludwig et al. 2016). e author oen treats the synovial structure as contaminated if the synovial fluid analysis is difficult to ascertain sepsis. Lastly, positive contrast radiography can help identify the tract if the offending object has been removed prior to arrival of the patient for diagnosis. Communication of the penetrating wound with any of the navicular bursa, DIP joint or DFTS can be demonstrated by infusion and distension of each respective synovial cavity with a radiopaque contrast agent. Following infusion of each synovial cavity a lateral radiograph should be obtained to determine if the cavity is intact, or if there is communication with the penetrating wound. e latter is evident radiographically as contrast material leaking from the synovial cavity along the penetrating tract (Figure 2) (Smith and Schramme 1992). Treatment Antimicrobial therapy is a key component of management of any deep penetrating injury to the foot. In selecting which antimicrobials to use, it is important to consider the likely contaminating organisms, and their pattern of antimicrobial sensitivity. e horses' environment is oen contaminated with soil and feces, and enterobacteriaceae and anaerobes are frequently indicated in infection following penetrating wounds (Snyder et al. 1987; Moore et al. 1992). is is particularly true for wounds involving horses' feet, which are oen heavily contaminated with both soil and feces. Systemic administration of antimicrobials is oen inadequate when eliminating infections, due to poor blood supply to the distal portion of the limb and insufficient synovial concentrations (Whithair and others 1992, Lugo and Gaughan 2006). Regional limb perfusion (RLP) is a well- known method for treating and preventing distal limb infection, which significantly decreases morbidity and mortality associated with trauma to these regions (Rubio-Martinez and Cruz 2006, Rubio-Martinez and others Figure 1: Lateral radiographic view of a foot with multiple nails showing possible structures penetrated based on location. (Photo courtesy of M. Smith) Figure 2: Contrast radiograph identifying communication of the penetration with the navicular bursa (Photo courtesy of M. Smith)

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